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From: Robert Klemme <shortcutter@googlemail.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: regex tidy
Date: Sun, 25 May 2014 18:49:41 +0200
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On 25.05.2014 18:09, Roedy Green wrote:
> On Sat, 24 May 2014 14:55:03 +0200, Robert Klemme
> <shortcutter@googlemail.com> wrote, quoted or indirectly quoted
> someone who said :

>>> 3. alphabetise | lists.
>> What does that mean?  Are you talking about merging common prefixes to
>> get a more efficient matching experience?  That might actually be done
>> by a regex engine if it detects this situation.
>
>
> (cat|rabbit|dog|cow)
> could be transformed to
> (cat|cow|dog|rabbit)
>
> for two reasons:
> make the list easier to proofread
> might help engine optimise handling the c in cat and cow in common.

The engine does not need the reordering to do this optimization.  If you 
want to help lesser engines which do not optimize here you would have to 
transform it into

(c(?:at|ow)|dog|rabbit)

to get more efficient matching.

Cheers

	robert